Two-stroke internal combustion engines



Jan. 28, 1964 P. M. ARMSTRONG TWO-STROKE INTERNAL COMBUSTION ENGINES Filed Sept. 21. 1962 a Attorneys PAW/0K Mqmcm 401145714 0116 United States Patent 3,119,380 TWO-STROKE INTERNAL COMBUSTION ENGINES Patrick Malachy Armstrong, 10 Bridewell Drive, Carrickfergus, Northern Ireland Filed Sept. 21, 1952, Ser. No. 225,293 Claims priority, application Great Britain Sept. 23, 1961 1 Claim. (Cl. 123-73) This invention relates to two-stroke internal combustion engines.

Various induction porting systems are employed in twostroke engines. The main ones are side porting, front rotary, rear rotary, rear disc, and reed or flutter valve. Each of these systems has certain disadvantages, for example:

(1) With side porting, induction is controlled by the piston and is of necessity of a very limited period, thereby limiting engine revolutions and consequently power.

(2) With front rotary, a large shaft is required which is weakened by having gas passages cut in it, and the machining of said passages adds to production costs.

(3) With rear rotary, a further rotating element is required which causes added drag, and adds to the cost of production.

(4) With rear disc valve, an extra rotating element is also required and the disc must form a close fitting seal against the backplate and must be exactly mounted to operate satisfactorily.

(5) With reed or flutter valve, the reeds are subjected to fatigue and as they only operate correctly at their natural frequency there is usually a loss of efficiency.

It is an object of the present invention to provide a two stroke engine having a porting system which obviates or mitigates all the above disadvantages of known systems.

The present invention is a two-stroke internal combustion engine, in which the opening and closing of the induction and/or transfer porting is controlled by the web interconnecting the crankshaft and piston connecting rod (hereinafter and in the claim referred to simply as the crankweb) Preferably, suitable induction and transfer ports are formed in the crankcase and the crankweb is suitably apertured, recessed or bored to act as a valve, whereby when each port and the crankweb aperture registers, passage of combustible mixture is allowed.

In the case of a twin cylinder or multi-engine, twostroke engine both crankwebs or either crankweb can be employed as aforesaid.

An embodiment of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which:

FIG. 1 is a perspective illustration of the crank case for a two-stroke internal-combustion engine according to the invention.

FIG. 2 is a sectional side elevation of the internal-combustion engine.

FIG. 3 is a sectional end elevation of the crankcase on the line III1II of FIG. 1, but with the carburetter mounted.

FIG. 4 is an elevation of the outer face of the crankweb.

The crankcase of a two-stroke internal combustion engine according to the invention is formed with an opentopped chamber 11, within the upper part of which the cylinder 12 is seated. This upper part is hereinafter referred to as the upper chamber and consequently the lower part is referred to as the lower chamber.

The crank case 10 is also formed with an induction passage 13 which runs transversely through a flange 14 in one side of the crankcase and terminates at its inner end, substantially mid-way down the lower chamber, in an elongated downwardly curved port 13A.

A transfer passage 15 runs vertically in the crankcase "Ice 10 between the upper chamber wall 11A and the outer wall of the crankcase 10 and terminates at its inner end, at the upper end of the lower chamber, in a curved, elongated port 15A which is similar to the induction port 13A and lies closely adjacent the upper end thereof.

The ports 13A and 15A have a common axis.

The outer end of the transfer passage 15 terminates at the top of the casing 10, the chamber wall 11A terminating slightly below the top of the casing so that the transfer passage 15 may communicate with a further transfer port 16 in the cylinder 12.

The induction passage 13 is in communication with a carbureter, for example, a spray bar carburetter 17 mounted in the crankcase flange 14 and extending across the induction passage 13. The upper end of the carburetter adjusting screw is secured to the cylinder to reduce vibration during operation of the engine.

A rotatable crankweb 18, the spindle 19 of which passes longitudinally through one wall of the crankcase 10, is located in the lower chamber and one face, of the web 18,

hereinafter called the inner face, closely abuts the face of the lower chamber in which the ports 13A, 15A are located. The opposite wall of the crankcase 10 may be in the form of a removable plate 10A to facilitate introduction of the crankweb.

The crankweb 18 is recessed on its outer face at 22 and carries a pin 20 adjacent its circumference for attachment to the piston crank 21. The crankweb 18 is also formed at or adjacent its periphery with a cut-away portion, slot or other through-aperture 23, hereinafter referred to as a through-aperture 23. The through-aperture 23, in the present example, is diametrically opposite the pin 20. In use, the through-aperture 23 registers with the induction port opening 13A to permit ingress of combustible mixture from the carburetter 17 into the crankcase 10. Rotation of the crankweb 18 in the direction of arrow R brings the through aperture into register with the transfer port 15A to permit transfer of the combustible mixture from the crankcase 10 to the cylinder 12.

The cylinder 12 has exhaust ports 24 and the crankcase 10 has cut-away portions 25 to accommodate the exhaust ports 24. The exhaust ports 23 are, as usual, controlled by movement of the piston 26.

The crankcase 10 has been hereinbefore described in its upright position for the sake of clarity, but it will be appreciated that, when mounted on a machine, it need not necessarily be placed in an upright position.

The two-stroke engine embodying the present porting system performs in the same manner as a conventional two-stroke engine.

With the present porting system, transfer control is no longer dependent on the position of the piston in the cylinder, being only related to it for the purpose of timing, so that it is now possible to locate the exhaust port lower ,in the cylinder for the same transfer period, thereby taking full advantage of the expanding gases and so increasing the efficiency of the engine.

The transfer port in the cylinder can now be located above the exhaust port, blow-down into the crankcase being prevented by arranging for the lower end of the transfer passage to be sealed by the crankweb until the exhaust port is uncovered by the piston. It can also be arranged for the transfer port in the crankcase to remain open until the piston passes the transfer port in the cylinder on the upstroke thus allowing transfer of the combustible mixture to continue even when the exhaust port is closed. This ensures a full charge of fresh mixture on each revolution.

The timing arrangements can be varied widely simply by either decreasing or lengthening the ports in the crankcase or the through-opening in the crankweb.

With the above described arrangement of porting more effective scavenging is possible, there is positive transfer, and the transfer port in the crankcase can be located to make best use of the centrifugal forces exerted in the crankcase.

The porting arrangement is applicable to all two-stroke engines, for example motor cycle engines.

It is especially but not exclusively applicable to model aero engines since,

the induction porting system also overcomes the aforesaid disadvantages of known systems, since (1) The induction period is not controlled by the piston.

(2) Ordinary shaft sizes are employed.

(3) By using existing rotating element (crankweb), no

extra member is necesary.

(4) No rear disc and therefore no special mounting.

(5 The induction action is positive and there is no danger of fatigue.

(6),It reduces production costs.

(7) It provides a more efiicient two-stroke engine.

Transfer control according to the invention offers the following advantages over other systems since:

(1) Transfer timing is not controlled by the piston.

(2) A longer period of transfer is possible for a given exhaust period.

(3) Locating the exhaust ports low in the cylinder, greater 4 use can be made of the expanding gases without any reduction in the period of transfer. (4) Asymmetric timing is now possible.

I claim:

An internal combustion engine comprising a crankcase having a cylindrical chamber communicating therewith, said crankcase having an interior plane surface disposed parallel to the axis of said cylindrical chamber, a spindle journaled in an opening communicating with the interior of said crankcase in said plane surface, said plane surface having an inlet port and an outlet port each disposed radially relative to the axis of said spindle, a crankweb formed integral on the interior end of said spindle having a face abutting said plane surface in sealing relation therewith, said crankweb having a connecting pin disposed parallel and spaced radially from the axis of said spindle, a piston head disposed in said cylindrical chamber for slidable movement therein, means for operatively connecting said piston head with said connecting pin, said crankcase having a transfer passageway intercommunicating the upper end of said cylindrical chamber and said outlet port, a fuel mixture intake passageway communicating with said inlet port and said crankweb having a single through opening registerable alternately with said ports.

References Cited in the file of this patent UNITED STATES PATENTS 666,264 Denison Jan. 22, 1901 861,673 Parnall July 30, 1907 2,179,683 Brebeck Nov. 14, 1939 FOREIGN PATENTS 1,061,504 France Nov. 25, 1953 841,827 Germany June 19, 1952 

